1. Technical Field
The present invention relates generally to central venous catheters, and more particularly, to a central venous catheter having enhanced pushability.
2. Background Information
Central venous catheters are typically used for medical procedures such as blood pressure monitoring, blood sampling and the administration of drugs and fluids to a patient. Such procedures often require that the catheter be left indwelling in the patient for an extended period of time.
Generally, a central venous catheter is surgically inserted into a major vein, such as the superior vena cava. Such catheters are typically introduced using percutaneous entry techniques, such as the well-known Seldinger technique. In the Seldinger technique, the physician makes an oblique entry into the vein with a beveled needle. A wire guide is then inserted through the bore of the needle about 5 to 10 cm into the vein. The needle is thereafter withdrawn, leaving the wire guide in place. The catheter is then inserted over the wire guide, and advanced through the skin at the needle puncture site and into the vein. Once the catheter is in place within the vein, the wire guide is withdrawn. The Seldinger technique is a widely used procedure for introducing catheters and other interventional devices into the vasculature, and is normally carried out by the physician without complication.
Since the central venous catheter is left indwelling in the vein, it should be soft and flexible in order to prevent erosion of the vein wall at the tip of the catheter. However, since the catheter is soft and flexible, it does not have a great deal of column strength. When a central venous catheter is pushed into a puncture site, it is not uncommon for the catheter to encounter some resistance. If the pushability of the catheter isn't sufficient to overcome this resistance, the catheter may “bunch up” or “accordion” at the site of the resistance. Certain portions of the catheter are particularly prone to bunching up. One such area is in the vicinity of the catheter sideports. When sideports are present in a catheter, the cross-sectional area and strength of the catheter at these sites is reduced, due in part to the lack of catheter material at the sideport. As a result, even more resistance to insertion is incurred at such sites, and the catheter may eventually become lodged such that it cannot be advanced further into the vein.
In the past, the problem of lack of pushability of such catheters has generally been addressed in two ways. The first way has been to form the catheter from a material that has a high enough stiffness or durometer to allow for good pushability in the vein, thereby enabling it to overcome the resistance encountered in the vein. However, increasing the stiffness of a catheter is generally undesirable and can compromise the safety of the patient by increasing the likelihood that the stiff catheter will eventually erode through the wall of the vein.
The second way to address the pushability problem has been to fill in the “dead space” in the lumens in the catheter, thereby imparting extra strength and pushability to the distal end of the catheter. The term “dead space” is used in the catheter art to refer to the portion of a lumen in a multi-lumen catheter, other than the central lumen, that extends distally from a sideport and terminates at a closed end near the distal tip. The dead space in a lumen can be filled with additional material that has a stiffness substantially the same as the stiffness of the catheter material itself. The additional material can be the same material as the catheter, or another compatible material having comparable stiffness. In one known process, generally referred to as “beading”, the additional material comprises beads that are inserted into the dead space at the sideport. Beading and similar approaches greatly increase the amount of material in the cross section at the tip area, and thereby make the catheter more pushable. However, the addition of beading to the dead space increases the stiffness of the tip area, even when the additional material is as soft as the catheter material itself. This increased stiffness increases the chance that the catheter tip will eventually erode the vein wall. In addition, the use of beading or extra plastic material to fill the space at the tip of the catheter is not an ideal solution because the addition of such material does not impart a great deal of extra column strength, and increases the stiffness of the catheter at the very portion that needs most to be flexible.
Central venous catheters generally have more than one lumen. Typically, such catheters have either two or three lumens. With multi-lumen catheters, one lumen may be used for pressure monitoring, another lumen may be used for drug or fluid infusion, and still another lumen may be used for blood sampling. The central lumen can additionally serve as the wire guide lumen during placement. As with other interventional devices, it is desirable that the lumens have the maximum cross-sectional diameter possible for a given catheter size so that optimal use can be made of available space. Thus, the amount of material utilized for the outer tube wall and the webbing between the lumens is preferably minimized to the greatest extent possible. However, minimizing the amount of material in the tubing wall and the webbing between the lumens also reduces the column strength, or pushability, of the catheter.
Accordingly, it is desired to provide a central venous catheter that has a high enough stiffness to allow for good pushability in the vein, and that does not involve the addition of a stiff catheter material or an appreciable amount of other material to the distal tip area of the catheter. It is further desired to provide a central venous catheter that has sufficient softness to minimize the possibility that the catheter will erode the wall of a vein.